TIDAL ACTION IN BRITISH COLUMBIA WATERS By CAPT. CHARLES WARREN CATES TIDAL ACTION IN BRITISH COLUMBIA WATERS By CAPT CHARLES WARREN CATES •• NORTH VANCOUVER CANADA 1952 C OPY RI G HT 1952 This little book which sets out to be the story of the massive, eternal tides is really the story of four men. Authored liy one man, Capt. Charles Cates, it was, in the truest sense of the word, inspired also by his father Charles Henry Cates, and his brothers John and James. You will draw much knowledge and pleasure from this book. The information is authentic. Let me tell you why. The three brothers grew up with the tides of British Columbia. The Cates family is part of the waterfront here. Old Charles Henry, a beloved figure, was towboating round here before the .boys wer,e born- in 1886. His first " tug" was a twin-screw scow, named Spratt's Ark. ·what an unbelievable story was her career! He went on from strength to strength, and so the boys as they came along grew up with the tugboating drama. John, Charles, James Cates . shipmasters the world over know them, have tm;ned to them for advice and help. You might well do the same by studying this book which contains the knowledge not of ·one man alone, but of four. The information is authentic also because all three brothers are certifi ed master mariners, with a lifelong experience of the movements of the great waters around this coast. But the little book also contains good stories of life on this coast. It is the first time in my long experience of the sea that I have seen the tides made clear and real to the layman. I comm end it to you, whether you are profes­ sional or amateur seaman. PAT TERRY, Marine Editor, Vancouver Sun CHARLES WARREN CATES The 1,1,--reck of the Beaver TIDAL ACTION IN BRITISH COLUMBIA W ATERS With cill the wo1iderfiil man-mcule forces being vroduced today, it is doubtful if nwny v eovle observe the huge natiwal phenomenum that is going on day in cind dciy out the yectr round, in ctll the oceans of the world. This is the tide, one of the grecitest forc es in the w01·/,d, involving the movement of coun,tless 1nillions of tons of water, bitt it moves so S'ilently and regiilarly) thctt I imag,ine most 'peovle never g'ive it ct thought. It has been known, I believe, as long as man has lived by the sea, because it was from the beaches exposed by the tide that much of his food was obtained. All along our coast in British Columbia are huge mounds or middens, acres in extent, composed of clam shell and the remains of other marine creatures that the people had collected for food. This can be seen by the charcoal and ashes of their camp fires, still to be found among the heaps of shells. The people of this coast had quite a culture of their own. They knew the movements of the principal stars and of the sun and moon. I don't know whether they connected their positions in the heavens with the tides, but they did have names for all the tidal movements, and_set their seasons by the moon. In other parts of the world it was doubtless the same. J ulius Caesar when first coming to Britain from the practically tideless Mediterranean , recorded that the rise and fall of the sea seemed to be governed by the moon . In fact at the present time the names of Spring Tide, which means a tide that is springing up, and a Neap Tide, which means decreased or inactive, have both come dow~ through the ages from ancient Saxon words. A,1 t he marine co mm erce of the world increased, it was natura.l - that more knowledge would be sought about the 9 movements of the oceans, as it is very important to a .shipmaster to know what t he tides are doing in any particular locality, at any given time. The first systematic and -thorough investigation of t he tides astronomically and mathematically was carried out by Laplace, and the French seem to have assun'led that t he influence of t he sun and moon being general, t he pattern would be the same everywhere, and that, accordingly, any one harbour would answer as a " Port of Reference" for all tides. In t heir early tide tables the "·hole world was t herefore referred to Brest. TIME DIFFERENCE It was, however, soon found that a constant differer.ce in ti.me from Brest gave entirely erroneous results in niany regions. This led to a scientific check by means of tide gauges, positioned all over the world. In Canada tidal investigation was begun in 1894, both on t he Atlantic and Pacific coasts, and the results are t he wonderfully accurate tide books that we lrnve today. They are resnHs of astronomical calculations, and carefully kept records of actual tidal conditions; but with all t his technical data, the scientists still admit t hat some tidal actions arc not thoroughly understood. As I understand it, t he rise and fall of the sea is go\·ernecl in the following manner: As both the sun anrl moon are relative to the earth, a ll three bodies have a gravitational attraction. In other words if t he earth were suddenly taken away, and some small earthly object left behind, that object would fall to the moon , as it has the next greatest gravitational attraction. In a similar manner if the moon were not t here, then t he object would fall or travel toward the sun.\ It can be readily understood t hen that as the moon and sun fo1·m rnrious combinations in t he heavens, so is t he attraction on t he earth strengthened or weakened. As t he oceans are fluid and able to move, they naturally flow towards t he point of greatest attraction. This causes a rise of water at t he point of greatest attraction. Also as the earth itself is attracted it can also move away from the body of water on the opposite side, that is to say the side farthest away from the gravitational pull. This then means that there are two bulges 10 of water on opposite sldes of t he world, and, as the world rotates once in twenty-four hours, produces two t ides per day. This, of course, would only be possible if t he moon and sun were in fixed p ositions, relative both to t hemselves and the earth. If the sun and moon were to stay in fixed positions over the equator, t hen the two tides per 24 hours would be eqnal. However, this is far from the case. Most people are familiar with t he movements of t he sun, an <.l how it travels across t he equator to t he Tropic of Cancer, which is 23 ° North in summer , and back to Capricorn which is 23° South, being its maximum travel. Also, how t he earth rotates once a day so as to expose its complete ciTcumference to t he sun once in 24 hours. 'l'IDAL EFFECT The moon has many more rnoY ements in r elation to t he earth which cause t he gravitational pull to vary 33 % from maximum to minimnrn, and as it h as more t han twice t he gravitational attraction of t he sun, its changes in position have a great effect on the tides. The m oo n's orbit is, properly speaking, an ellipse, bnt the ancient G1·eeks dcsci-ibcd it as a circle with the earth a little ont of the middle. The point where the moon is nearest to the earth is P erigee. and the point where it is .farthest a way is Apogee. The period of rotation from Perigee to P erigee is called t he Anornalistic 111 011 th. Its length is slightly orer :!71/~ days. The motion of the iu oou in its ol"bit is n ot uniform, ho\\·ever, but it trar els faster t hrough Pe1·igee and more slowly when near Apogee. Thi s ca uses t he moon to be r, 2ai-ly one hour later each cl ay rclati1·e to the sun's position. This cycle is what canse;:, t he time of high water to becorn e later each day. It can be readily 1111de1·stoocl t hen, t hat while t he snn ancl 1noon are in a favournbl e position, relative to each other, tlw attraction will be great, but as they swing so as to pnll on tlw quarter to each other, the pnll o[ one will be opposed to the other . As t he movement of t ide is a wa ve action, and the true 0 1· mean level of t he sea. is midway between t he level of hi gh and lo,1· water, or in other words, t he t ide fall s a.s mnch below t he rn ea11 or undisturbed level as it rises above it, then a slight change in attraction will be qnite noticeable jn its effect on t he tide. 11 As I have said, the moon has many movements, one of which the movement north and sonth across the equator has great effect on the tide. This action is similar to t he sun, with the exception, that while the sun ma kes the journey once a year, the moon crosses the equator twice in less than one month.